Introduction

One of the new features of F15 will be the introduction of a Cross Compiler Framework.
This framework will obsolete the Fedora MinGW toolchain which can be found in current versions of Fedora.

Initially, this framework will have support for building binaries for Win32 and Win64 targets.
The mingw-w64 toolchain will be used for this. However support
for other targets (like Mac OS X) can be added quite easily.

The goal of this framework is to provide a generic method to cross-compile binaries for multiple targets with as little packaging overhead as possible.

Namespaces

The framework will use several namespaces. Each namespace has it own characteristics. These will be explained here

Package names:

cross- Used for packages which can be built for multiple targets
mingw- Used for packages which can be built for both Win32 and Win64 but not for other targets
mingw32- Used for packages which can only be built for Win32
mingw64- Used for packages which can only be built for Win64
darwinx- Used for packages which can only be built for Mac OS X (future work)

Filelists:

%{_cross_...} Used for files which are common among all possible targets
%{_mingw_...} Used for files which are used on both Win32 and Win64
%{_mingw32_...} Used for files which are only used on Win32
%{_mingw64_...} Used for files which are only used on Win64

A yum testing repository containing binaries for all packages is available now.
To enable this repository, drop the file http://build1.openftd.org/fedora-cross/fedora-cross.repo in /etc/yum.repos.d and perform a 'yum update'.
Note that this testing repository will obsolete any mingw32 packages you might have installed!

Issues with this testing repository can be reported on the fedora-mingw mailing list or #fedora-mingw on FreeNode

Roadmap

To provide a clean upgrade path and as little breakage as possible the introduction of this framework can be split in several phases.

Phase 1: Get the mingw-w64 toolchain in Fedora

The keep the amount of breakage as low as possible all these 5 packages have to be imported at once.

Phase 2: Bootstrap the mingw-w64 toolchain

Once the 5 packages mentioned in phase 1 are approved they can be imported. In order to bootstrap the mingw-w64 toolchain this has to be done in a specific order.

1. Import the cross-filesystem package, build it and wait for it to enter the buildroot
2. Import the cross-binutils package, build it and wait for it to enter the buildroot
3. Import the mingw-headers package, build it and wait for it to enter the buildroot
4. Import the cross-gcc package, build it (with the %bootstrap flag set to 1) and wait for it to enter the buildroot
5. Import the mingw-crt package, build it and wait for it to enter the buildroot
6. Rebuild the cross-gcc package with the %bootstrap flag set to 0 and wait for it to enter the buildroot

Phase 3: Rebuild all mingw32 packages

The mingw-w64 toolchain is now operational and can build binaries for both Win32 and Win64.
As the name of the triplet has been changed (in the cross-filesystem package) from i686-pc-mingw32 to i686-w64-mingw64 as mingw32 packages have to be rebuild.
All mingw32 packages should have been using macros like %{_mingw32_bindir} as mentioned in the MinGW Packaging Guidelines.
As all these macros have been moved to the cross-filesystem package (and some deprecated macros are kept for backwards compatibility) a plain
rebuild should be sufficient to get mingw32 packages built against the new toolchain.

Packages which have the triplet 'i686-pc-mingw32' hardcoded in their .spec files need to updated as they aren't conforming to the packaging guidelines

Phase 4: Drop the old mingw32 toolchain packages

Now that the mingw-w64 based toolchain is imported the original mingw32 based toolchain has been obsoleted.
The packages mingw32-filesystem, mingw32-binutils, mingw32-gcc, mingw32-w32api and mingw32-runtime can be dropped from the repository without breaking anything

Phase 5: Rename and port all mingw32-packages to the new framework

This phase is also the most time-consuming one. Right now all mingw32 packages use the prefix 'mingw32-'.
All packages (which want to be built for both win32 and win64) have to be renamed to use the prefix 'cross-' instead of 'mingw32-'.
In additional several macros will have to be replaced. See the porting guide for more details.

This phase isn't time limited. Package maintainers don't have to port to the new framework if they don't want to add support for additional targets. They can leave their packages as is

Porting guide

First thing to keep in mind is that the name of the triplet for Win32 has been changed. Originally this was i686-pc-mingw32 while with the new cross compiler framework this has changed to i686-w64-mingw32.
This has been done to indicate that the new mingw-w64 toolchain is used instead of the old mingw.org one.
All paths have been updated to use this new name as well. So now all files are kept in /usr/i686-w64-mingw32 instead of /usr/i686-pc-mingw32 for Win32.
After the initial rebuild (as mentioned in phase 3) all files will be moved to this new location.

If you want your package to be built for multiple targets instead of just Win32 you need to rename the package to use the 'cross-' or 'mingw-' prefix (depending on the package) and apply some changes in the .spec file.
If you don't want to add support for other targets you can leave the .spec file as is and ignore the rest of this porting guide.

Generic macros

Most Fedora MinGW packages contain this set of instructions at the top of the .spec file:

Packages containing macros to generate debuginfo subpackages should also update the call to %{?_mingw32_debug_package} to %{?_cross_debug_package}

Upgrade path

To provide a clean upgrade path for users who already have the mingw32 version of your package installed you need to add an 'Obsoletes: mingw32-mypackage < x.y-z' to your .spec file

Build targets

To indicate which targets you want to have the package build you need to add one of these (or all) lines to your .spec file.
To build for Win32:

%global _cross_build_win32 1

To build for Win64:

%global _cross_build_win64 1

Description and Summary

Most packages mention in their description and/or summary that the package in question is targeted for Win32. Though not strictly required, it's recommended to update the description and summary tags to indicate the targets which this package supports

BuildRequires

As a new 'cross-' prefix has been introduced for the base toolchain packages the BuildRequires have to be updated:

For other dependencies it depends on whether that specific package has been ported to the new cross compiler framework

Running the ./configure script

The original Fedora Mingw toolchain contained a macro called %{_mingw32_configure} which could be used to call the ./configure script with the proper arguments set.
For cross compilation to multiple targets a new macro has been introduced called %{_cross_configure}.
The macro creates a separate folder for each target (out of source compilation) and executes the configure script for every target (set with the flags mentioned earlier).

Almost all packages support out of source compilation or require slight patching. The only known exceptions to date are zlib and openssl.
Packages which don't support out of source compilation may require a different approach like performing everything in the %install phase.
If you happen to stumble across a package which requires a different approach feel free to contact us on the Fedora MinGW mailing list

If you want to supply arguments to the ./configure call, you have to use a slightly different approach than before.
Say you've got something like the call below:

%{_mingw32_configure} --disable-xlib --enable-win32

This has to be changed to something like this:

%{_cross_configure "--disable-xlib" "--enable-win32"}

The quotes mentioned above are mandatory! If you forget them then rpmbuild will fail or the arguments might not get passed to the ./configure calls.
Also note that the '}' character needs to be placed after all the arguments

Some packages need to be built multiple times for each target. Examples of this are packages which have to be built once for a static version and once for a shared version.
Such packages can add a custom suffix to the build directory used.
Say you've got something like below:

Building and installing the package

Most packages used the command 'make %{?_smp_mflags}' to build the package.
In the cross compiler framework you have to use '%{_cross_make %{?_smp_mflags}' to build the package for all configured targets
As with the %{_cross_configure} macro you can also use the '-s' argument to indicate a custom suffix to the build directory used

To install the package the command 'make install DESTDIR=$RPM_BUILD_ROOT' was used in almost all cases.
This can be rewritten to '%{_cross_make_install DESTDIR=$RPM_BUILD_ROOT}' to install the package for all configured targets
The '-s' argument can also be used here

Custom %install instructions

Some packages require some custom instructions before the files are ready to be packaged.
Such code can remain as is. However, you may need to duplicate these instructions multiple times (for all configured targets).

File lists

All the original filelist macros from the original Fedora MinGW toolchain (like %{_mingw32_bindir}) are still available.
However, when adding support for multiple targets these macros aren't sufficient.
To create filelists which support multiple targets you can use a different set of macros as can be seen at the namespaces chapter.